New York City is a unique source for naturally occurring cat and dog tumors. Unlike tumors in man, most of these animals have not been treated with any form of immunosuppressive therapy and they are therefore ideal for elucidating the effectiveness of immunotherapy for cancer. The biological behavior of naturally occurring tumors in cats and dogs is still unknown. One of the primary objectives of this study will be to determine the biological behavior of a variety of tumor types, both with and without therapy. The effectiveness of different therapies, especially immunotherapy, for naturally occurring tumors of pet cats and dogs will be studied. The following tumors will be studied in detail: feline mammary tumors, canine mammary tumors, canine oral melanomas, and feline and canine lymphosarcoma. The effectiveness of surgery alone, and surgery combined with levamisole immunotherapy for feline and canine mammary tumors will be studied. Canine oral melanomas will be treated with cryosurgery alone or with C. parvum immunotherapy. Dogs with lymphosarcoma will be treated with chemotherapy, either alone or in combination with levamisole immunotherapy. The results we have obtained with the treatment of feline lymphosarcoma with blood constituents indicate that normal blood constituents have an antileukemic activity. We propose to investigate this phenomenon further and elucidate the mechanisms responsible for this activity. In addition to the primary objectives, the effects of other immunotherapeutic agents such as mixed bacterial vaccine and thiabendazole will also be studied.